The glass contacting surfaces of glass forming equipment need to be lubricated to prevent the glass from sticking to the surfaces. Various methods have been used to provide the needed lubrication, usually in the form of a carbon layer on the glass contacting surfaces.
For decades, glass manufacturers have lubricated glass contacting surfaces by dabbing them intermittently with a suspension of graphite in oil. When the hot glass contacts the dabbed surfaces, the oil is burned leaving a graphite coating on the surface. This has been demonstrated to provide acceptable lubrication to prevent glass from sticking to the surfaces but the method suffers from a number of drawbacks. The manual dabbing of mold surfaces is labor intensive and is fraught with danger from the close proximity between operators who apply the oil and graphite to the glass contacting surfaces and the hot glass and the hot glass forming equipment. In addition, the oil in which the graphite is suspended burns when contacted by hot glass. This oil combustion is not complete and, as a result, substantial amounts of smoke and soot are produced when this lubricating method is used. The problems of smoke and soot are especially dangerous in wood buildings where smoke and soot rise with the hot air currents and form deposits on the roof and rafters. Roof fires are a common and pervasive problem in glass factories where oil and graphite lubricants are used. Some factories are known to have fires every few months, despite the fact that the roof and rafters are sprayed with water, regularly. Aside from the problem with fires, oil and graphite lubricants create substantial pollution problems which are subject to increasingly stringent controls.
U.S. Pat. No. 4,806,137 discloses the use of a hydrocarbon containing fuel mixed with large volumes of oxygen to lubricate the glass contacting surfaces of glass forming equipment. According to the patent, at least one gaseous hydrocarbon is injected through an oxyfuel flame having a temperature higher than 2000 degrees Kelvin to produce a porous layer of carbonaceous particles on the glass contacting surface. The carbon layer deposited on hot glass is said to be capable of burning in air.
U.S. Pat. No. 4,498,918 discloses the use of a mixture of methyl acetylene and propadiene (hereinafter "MAPD gas") and at least one hydrocarbon having an acetylenic triple bond to lubricate a mold cavity. The patent does not disclose or suggest the use of a mixture of MAPD gas and oxygen to lubricate glass contacting surfaces.
U.S. Pat. No. 5,679,409 discloses a method for lubricating glass contacting surfaces of glass forming equipment. The method comprises the steps of delivering MAPD gas to a venturi at a low pressure, preferably below 10 p.s.i., and delivering oxygen to the venturi at a lower pressure, usually half or less than half of the pressure at which the MAPD gas is delivered to the venturi. The MAPD gas and the oxygen are mixed in the venturi and delivered to and through a nozzle which is directed toward a glass contacting surface. The mixture is ignited as it leaves the nozzle; its flow is controlled so that the temperature of the flame is between approximately 1500 and 1800 degrees K. By controlling the temperature of the flame, the method is operable to deposit on the glass contacting surface a lubricating coating of graphite including a substantial percentage of flat plate graphite. In some situations, for example, lubricating conveyor belts for transporting hot glass, natural gas is substituted for the oxygen and lubrication is achieved with less use of the MAPD gas.